J. Nannoplankton Res. 37 (2–3), 2017, pp.245–251 © 2017 International Nannoplankton Association
ISSN 1210-8049 Printed by The Sheridan Press, USA245

Evaluation of the biostratigraphy of the CretaceousPaleogene boundary interval in the Hendijan oil field,
Zagros (SW Iran)
Saeedeh Senemari*Department of Mining, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran. Tel: +00982833901126-09127852086(Fax): + 00982833780073; senemari2004@yahoo.com

Marziyeh Notghi Moghaddam
Department of Geology, Payam-e Noor University, Tehran, I R of Iran; m.n.moghaddam@gmail.com
Manuscript submitted 2nd November, 2016; revised manuscript accepted 29th July, 2017

Abstract The Zagros Basin is part of the Neo-Tethys Basin in Iran and includes three stratigraphic provinces.

Exploration studies in this basin are very important due to the presence of large hydrocarbon fields, such as theHendijan oil field, where The Gurpi and Pabdeh Formations are significant source rocks. This study examines
the calcareous nannofossil biostratigraphy of the upper Gurpi Formation and 66m of the Pabdeh Formation in acontinuous core taken from a well in the Hendijan oil field, located in southwest Zagros. The 33 genera and 50 speciesof calcareous nannofossils identified in these samples clearly delineate the Cretaceous/Paleogene boundary in thisoil field. In this core, the upper Gurpi Formation spans the upper Lower Maastrichtian to lower Upper Maastrichtian(Zones CC24-25). The overlying Pabdeh Formation is assigned to the terminal Middle Paleocene to Upper Paleocene(Zones NP6-9).

Key words biostratigraphy, calcareous nannofossils, Cretaceous, Paleocene, Paleogene, Hendijan, Zagros
1. Introduction
A thick Phanerozoic sedimentary sequence (CambrianRecent) was consistently deposited in a subsiding troughin the Neo-Tethys (Darvishzadeh, 1992). The collision of
the Arabian Plate and Central Iranian Block during theMesozoic and Cenozoic produced the Zagros fold belt,
which contains more than 10,000m of post-Paleozoic
strata. The fold belt extends NW-SE for about 2000km
from SE Turkey through SW Iran (Motiei, 1995; Alavi,
2004; Kamali et al., 2006) and is one of the largest known
oil fields. It has been referred to as the “Agreement Area”
since 1954. The Gurpi Formation (Fm) and Pabdeh Fm
are exposed throughout most of the Agreement Area insouthwestern Iran; both formations are present in all threeprovinces (Khuzestan, Lurestan and Fars) in the Zagros
fold belt (Kamali et al., 2006). The name, Gurpi, derives
from the Kuh e-Gurpi in Khuzestan Province, and its typesection in North Lali oil field (NE Masjed Soleiman) is
comprised of argillaceous limestones with shales and graymarls. In North Lali oilfield, the Gurpi Fm overlies theIlam Fm and is disconformably-overlain by the Pabdeh
Fm. The name of the Pabdeh Fm is derived from Kuh
e-Pabdeh in Khuzestan Province, where James & Wynd
(1965) described the type section at Tang e-Pabdeh inNorth Lali oilfield, which consisted of shales and argillaceous limestones with marls. The lithologies of the
Gurpi and Pabdeh Fms are very similar, making their
distinction in the field nearly impossible and microscopic
studies (e.g., calcareous nannofossils) a necessity. These

formations have previously been investigated by various aspects of paleontology (e.g., Mohseni & Al-Aasm,
2004; Khosrowtehrani, 2008; Bahrami, 2009; Behbahani
et al., 2010). The calcareous nannofossil biostratigraphyof various formations in the Zagros Basin have also beenstudied in recent years (e.g., Hadavi et al., 2007; Senemari& Sohrabi Molla Usefi, 2013). The current study is thefirst to detail calcareous nannofossil assemblages acrossthe Cretaceous/Paleogene (K/Pg) boundary interval in theHendijan oilfield. The main purpose of our research is toestablish correlations to global biozonations and evaluate
paleoecologic conditions for the study area.
2. Material and methods
The Hendijan oilfield is located in the northwestern Persian Gulf on Dezful Embayment. The sequence considered is located in the SE Dezful Embayment, about 170km
southeast of Ahwaz, between 49.5–50ºE longitude and
30–30.75ºN latitude (Figure 1). Sediments of the upper
Gurpi and Pabdeh Fms were selected to investigate theK/Pg boundary interval using calcareous nannofossils.
The studied section is an 80m continuous core that consists mainly of shales, marls and shaley limestones. Lithologies (argillaceous limestone, shale and marl) transitional
between the Pabdeh Fm and the overlying Jahrum Fm
are present near the top of the core. Seventy-eight samples were collected systematically in intervals between
50–100cm throughout the Gurpi and Pabdeh Fms. Only
one sample was taken from the overlying Jahrum Fm.

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Figure 1: A: Generalized map of Iran showing eight geologic provinces, adapted from Heydari et al. (2003); B: Locality map of the studied area,
Hendijan oil field

Samples were prepared by the standard smear slide
method (Bown & Young, 1998) directly from raw samples
and rock fragments without centrifuging. All slides werestudied under cross polarized light (XPL) and phase contrast (PC) at a magnification of 1000X using an Olympus
microscope.
Calcareous nannofossil taxonomic concepts followed
Perch-Nielsen (1985a, b) and Bown (1998). Nannofossil
assemblages represent counts of the first 100 fields ofview (FOV) and are presented in Table 1 as follows:
R = rare (1 specimen per 11–100FOV); F = few (1 specimen per 2–10FOV); C = common (1–10 specimens per
FOV); A = abundant (>10 specimens per FOV). At least
300 specimens were counted in each sample for paleoecologic and biostratigraphic discussion. To avoid enlarging
Table 1, each row in Table 1 represents three samples.
3. Biostratigraphy
Results from studied samples show the nannofossil biostratigraphy of the upper Gurpi and Pabdeh Fms relative
to the K/Pg boundary (Table 1). A total of 17 genera and27 species were identified in samples from the Gurpi Fm,
while 17 genera and 24 species were identified from samples in the Pabdeh Fm and the base of the overlying “Transitional Zone” to the Jahrum Fm. A major disconformity
separating the “mid” Maastrichtian Gurpi Fm and Upper
Paleocene Pabdeh Fm has been linked to epeirogenic
movements in the Zagros fold belt (James & Wynd, 1965;
Motiei, 1994). We estimate the disconformity identified in
the core encompasses about nine million years, using thetime scale of Gradstein et al., (2012).
We apply the CC zonation of Sissingh (1977, 1978)
for the Cretaceous Gurpi Fm, whereas both the NP zones

of Martini (1971) and CP zones of Okada & Bukry (1980)
are applied to the Paleogene Pabdeh Fm. Other main references are used (Perch-Nielsen, 1985a, b; Burnett, 1998;
Self-Trail, 2001) for Maastrichtian to Paleocene nannofossil biostratigraphy and their calibration to the Geologic
time scale of Gradstein et al., (2012). Abbreviations usedherein are FO for the first occurrence and LO for the last
occurrence. Several of the species identified in this study
are illustrated in Plates 1–2.
3.1 Biozonation of the upper Gurpi
Formation
The Reinhardtites levis (CC24) and Arkhangelskiella cymbiformis (CC25) Zones have been identified in samples
from the Gurpi Fm (Table 1). The total thickness of thebiozones CC24 (6m) and CC25 (9m) is 15m. The LO of
R. levis marks the boundary between these two zones andis a rough approximation for the top of the Lower Maastrichtian (see Gradstein et al., 2012). The base of Micula
praemurus was observed in the same core sample as thehighest occurrence of R. levis. Self-Trail (2001) placed
the FO of M. praemurus near the base of Subzone CC25a.
The core is thought no older than Zone CC24 because of theabsence of Tranolithus orionatus (= T. phacelosus), whose
extinction marks the top of Zone CC23. Lithraphidites
quadratus and Micula murus were both observed in thehighest sample from the Gurpi Fm. The FOs of these
two species have been utilized as the base of Subzones
CC25b/c by various authors (Sissingh, 1978; PerchNielsen, 1985a, Self-Trail, 2001). Micula praemuruswas also observed in this top sample. Self-Trail (2001)
reported the LO of this species within Subzone CC26a.
The absence of Micula prinsii, which marks the base of

…the Cretaceous-Paleogene boundary interval in the Hendijan oil field, Zagros…

247

Table 1: Stratigraphic chart of Gurpi and Pabdeh Formations based on Calcareous Nannofossils, Hendijan oil field located Southwestern Zagros.
Braarudosphera bigelowii is identified in both Fms. Species abundance: R = rare (1 specimen per field of view [FOV] 11–100), F = few (1 specimen
per 2–10FOV), C = common (1–10 specimen per FOV), A = abundant (>10 specimen per FOV)

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Subzone CC26b (Self-Trail, 2001), is further evidence thatthe terminal Maastrichtian is absent in the core.
3.2 Biozonation of the Pabdeh Formation
The following succession of biozones was recognized in
the Pabdeh Fm: Heliolithus kleinpellii Zone (NP6/CP5),
Discoaster mohleri Zone (NP7/CP6), Heliolithus riedelii(NP8)/Discoaster nobilis (CP7) Zone, and Discoastermultiradiatus Zone (NP9/CP8). The total thickness of the
Paleocene biozones NP6 (19m), NP7 (14m), NP8 (12m)and NP9 (20m) is 65m. The single sample from the overlying “Transitional Zone” contains Tribrachiatus bramlettei,
which marks the base of the T. contortus Zone (NP10/CP9) and approximates the base of the Eocene. The lowest
sample in the Pabdeh Fm contains H. kleinpellii, the FOof which marks the base of Zone NP6 (CP5). Sphenolithus
anarrhopus is also present in this sample. The FO of thisspecies was placed in mid-Zone NP6 by Perch-Nielsen(1985b). The FO of D. mohleri marks the base of Zone
NP7 (CP6) and is observed in the next sample up section.
The base of Zone NP8 (NP7) is approximated by the lowest occurrence of D. araneus in the core (Table 1). The baseof Zone NP9 (CP8) is identified by the base of the marker
species, D. multiradiatus. Three other events are coincident with the base of D. multiradiatus in the core: the basesof F. lillianae and R. cuspis, and the top of H. kleinpellii.
4. Paleoecology
Recovered nannofossil assemblages are indicative of open
marine conditions and a deep marine environment (Okada/ ")F,e^ D<=Z& .G+L^ D<==& 8HG,i / TI,G*`i1^ CZZ'& JLL+
et al., 2004; Thierstein & Young, 2004; Dunkley Joneset al., 2008). Several have low-latitude (i.e. warm water)affinities, such as Discoaster, Ericsonia, Fasciculithus andSphenolithus (Bralower, 2002; Gibbs et al., 2006; SelfTrail et al., 2012; Villa et al., 2008). Also of significanceare common B. bigelowii in the bottom two samples of the
Pabdeh Fm, which could indicate nutrient enrichment and/or
eutrophic environments (Konno et al., 2007) for Zones
NP6-NP7. In the Cretaceous, high abundances of certain
taxa (A. cymbiformis, Watznaueria barnesiae, Eiffellithus
turriseiffelii and Ceratolithoides aculeus) could be evidence for oligotrophic surface waters (Thierstein, 1976;
Watkins et al., 1996; Lees, 2002; Herrle, 2003; Bown
et al., 2004; Kaya Ozer, 2014; Linnert & Mutterlose,
2009; Thibault & Gardin, 2010); however, this abundance
may also be explained by poor preservation.
5. Conclusion
In this study, 33 genera and 50 species of calcareous nannofossil have been identified in a detailed study of an 80m
core from a well in the Hendijan oilfield. Six calcareous
nannofossil zones have been recognized in the Gurpi and
Pabdeh Fms present in this core. As expected, calcareous
nannofossil assemblages show a significant change acrossthe K/Pg boundary. This change is exaggerated by a major

disconformity between the two formations, where theearly Late Maastrichtian (CC25) Gurpi Fm is overlain by
the latest Middle Paleocene (mid-Zone NP6) Pabdeh Fm,
giving a disconformity of ~9My.
Acknowledgements
The authors would like to thank both manuscript reviewers and Dr. Jamie Shamrock for her comments that helped
improve the manuscript.
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Plate 1

Plate 1: All figures in XPL except figures 5, 9, 10 in PPL, light micrographs ×2500

…the Cretaceous-Paleogene boundary interval in the Hendijan oil field, Zagros…

Plate 2

Plate 2: All figures in XPL except figure 1 in PPL, light micrographs ×2500

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